These cases heralded the onset of epidemic cholera, with subsequent rapid spread throughout the country, facilitated by the major disruptions of the public health infrastructure associated with the January 12, 2010, earthquake. In this setting, there is a critical public health need to better understand cholera transmission in Haiti, and assess the possible future course of the disease on the island and the impact of various proposed interventions. At a more general level, the Haiti situation provides an ideal setting to monitor the transition from of cholera from epidemic to endemic disease, with a focus on understanding development of environmental reservoirs, routes of transmission, risk factors for illness, and evolutionary changes within the microorganism itself. We would note, in particular, the uniqueness of the situation, with the apparent clonality of the infecting strain providing an opportunity to follow development of strain diversity across time, with a known starting point (October, 2010), in an island setting where there has been no cholera for over 50 years. To address these issues, we are proposing a series of studies based in the Gressier region of Haiti, where the University of Florida has had ongoing relationships with communities and community leaders for close to 15 years, and where our College of Public Health and Health Professions is completing construction of a microbiology laboratory/research facility. Specific aims of the project will include the following: 1) Identification of V. cholerae in household members and in the environment: this will include surveillance in a school-based cohort of approximately 1,200 households, with follow-up of all diarrheal episodes by culture, and monitoring of all family members (symptomatic and asymptomatic) for a 4 week period after each family index case; and identification and systematic monitoring of household water sources and environmental reservoirs for V. cholerae. 2) Assessment and comparison of evolutionary changes in clinical and environmental V. cholerae isolates, making use of VNTR and whole genome SNP analysis. 3) Further refinement and validation of mathematical models of cholera transmission, including assessments of the impact of immunization and other interventions on transmission. Activities will focus on agent-based simulation models, using data from the field studies in Gressier for calibration. Models will be integrated into public health efforts to anticipate progression and transmission of cholera in Haiti, and the impact of proposed interventions.